Polymer electrolyte membrane fuel cells (PEMFCs) currently used among a variety of fuel cells have many advantages of low operation temperature and high energy efficiency and research is thus continuously underway on use of PEMFCs as power sources of vehicles.
That is, polymer electrolyte membrane fuel cells (PEMFCs) have advantages of high current density, low operation temperature of 60 to 80° C., and little corrosion and electrolyte loss, as compared to phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs) and the like.
In addition, the polymer electrolyte membrane fuel cells can stably supply power owing to benefits such as low cost, low volume, long stack life, and fast start-up and suitability for discontinuous operation and are thus utilized in a variety of applications including vehicles.
A membrane electrode assembly (MEA), which is a basic unit of the polymer electrolyte membrane fuel cell, is operated based on the following principle. A hydrogen ion produced by oxidation of hydrogen at an anode moves to a cathode via a polymer electrolyte as a medium and produces water by reduction with oxygen and an electron on the cathode, thus generating electricity (see FIG. 1). Oxygen reduction reaction having much higher activation energy than hydrogen oxidation reaction corresponds to a rate-determining step in a fuel cell and is an obstacle to the improvement of fuel cell performances.
Recently, as the demand for decrease in platinum catalyst amounts increases, improvement of performance of electrodes with low amounts of platinum catalysts has been an issue and active research is underway in order to improve oxygen transfer which should be considered upon using electrodes with low amounts of platinum catalysts.
Accordingly, there is a need for novel technologies that can facilitate oxygen transfer, prevent sulfone groups of an ionomer from being confined to a metal catalyst surface and thereby improve transfer of hydrogen ions by restricting a formation of an ionomer coating film on the metal catalyst surface, that is, that can improve the capability to transfer both oxygen and hydrogen ions based on spatial dualization of transfer routes for hydrogen ions and oxygen by controlling distribution of the ionomer in the electrode.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.